In our lab, we are looking to identify neural crest genes that are important in early craniofacial development. It has previously been shown that both cranial and trunk neural crest cells can give rise to several different cell types. However, only the cranial neural crest cells are capable of differentiation into craniofacial mesenchyme to give rise to bone, muscle and connective tissues. Our hypothesis is that selective gene expression in the early cranial crest allows cranial mesenchymal differentiation To test this hypothesis, we first generated cDNA of chick cranial and trunk neural cell outgrowths from neural tube explants. This was done via the reverse transcriptase PCR reaction in which the RNA is converted into cDNA containing amplimer ends for facilitation of PCR amplification. The cDNA was then screened utilizing specific primers to check for integrity. The cranial cDNA is now being utilized for differential mRNA display screening to identify cranial crest specific genes. We have been able to tentatively identify several cDNAs that are differentially expressed in the cranial crest cells. At this time we are continuing to characterize these genes via in situ hybridization utilizing the cloned cranial crest specific cDNAs. These in situ hybridizations are differential for the cranial neural crest (and the cardiac subdivision of the cranial crest). Corroborating evidence is provided by slot blot analysis. All of the evidence accrued thus far points to a genetic event, as yet, not fully characterized, which is confined to the cranial neural crest. In the future, the goal will be to evaluate the role of these genes in craniofacial development. Fully 75% of all birth defects are found in the craniofacial complex. It is to this and that we will then isolate the mammalian homologue for transgenic mouse studies and human genetic mapping of birth defects involving craniofacial development. The ability to map these and other differentially expressed genes of the cranial neural crest will allow us to understand the control of cranial crest cell differentiation and ultimately, permit us to apply this knowledge to the study of cleft palate and other craniofacial abnormalities.